Added Critically Triangular.
Aaah, the joys of trigonometry!

Also added Word Snake, which doesn't currently have any solutions, because I'm not sure how I could do that!
It's an open-ended game, and should at least prove somewhat challenging.

In addition, I've also rejigged the puzzle selection menu to make it a little bit neater, sectioning off the games into their various categories, and I've also shuffled the How To instructions to be in the same order.